Various types of triggering systems for seatbelt locks, airbags, and the like, have been proposed; one such construction is described in the referenced literature. In such systems, typically, an acceleration sensor--or, more accurately, a deceleration sensor--determines deceleration of the vehicle and provides a deceleration output signal to an evaluation or control circuit if the vehicle deleration corresponds to an impact on an obstruction which may be another vehicle. The triggering system electrically triggers an ignition which, by chemical reaction, or explosion, causes sudden inflation of an airbag, or immediate tightening of a seatbelt or seatbelt system, such as a combination lap-shoulder belt, or the like.
The system, thus, uses two distinct and discrete elements: the electrical sensing system and, then, a chemical or other triggering system since, after the initial sensing which is carried out with electronic speed, electrical power may no longer be available due to destruction of the electrical system or interruption of electrical circuitry.
If various passengers are present in the vehicle, or if the vehicle, in general, is equipped for several passengers, particularly for at least four passengers, individual triggering circuits for the seatbelts or airbags--in general, passenger restraint units--may be provided. Since the life of the passengers may well depend on the operability of the overall system, it is necessary to test the various components at suitable intervals, for example each time an oil change or other maintenance of the vehicle is carried out. Testing of the control system themselves is known--see, for example, Published European Patent Application EP-A 11 680, or EP-B 22 146; the checking and testing of the control or evaluation unit, itself, does not form the subject matter of the present invention. Rather, the present invention is directed to testing of the triggering or ignition circuits which cause explosion or other chemical reaction of the restraint unit itself.
In accordance with customary use, a common return line is used for the trigger elements of each of the separate, for example, four, restraint units. This, then, requires, for safety and functionality, five connecting lines: four for the four triggering circuits, and one return line. It is, then, necessary to additionally provide control units with five circuit connectors in order to test the respective ignition trigger circuits after installation. In customary commercial plug pins, it is only possible to connect, at the most, two connecting lines at a time. The number of connecting lines, thus, is quickly multiplied, and will increase to six.